Inhibition of systemic onset of post-transcriptional gene silencing by non-toxic concentrations of cadmium

Post-transcriptional gene silencing (PTGS) is an important mechanism for re gulation of plant gene expression and virus-plant interactions. To better u nderstand this process, the heavy metal cadmium was identified as a specifi c inhibitor in two different PTGS systems, constitutive and inducible. The pattern of cadmium-induced inhibition of PTGS allowed several insights into PTGS development. First, cadmium treatment prevented only systemic but not local onset of PTGS, uncoupling between these two modes of PTGS. Second, n on-toxic, but not toxic, levels of cadmium inhibited PTGS, suggesting induc tion of a pathway that interferes with PTGS. Third, cadmium effects on PTGS closely paralleled those on the movement of tobamoviruses, suggesting that both processes may share common steps in their systemic transport pathways . Interestingly, these effects of cadmium do not represent a general proper ty of toxic metal ions because two other such elements, that is zinc and al uminum, did not interfere with PTGS and viral systemic movement.